The present invention relates to a method and an apparatus for applying silicone oil (hereinafter referred to simply as silicone) to a back end of a injection needle comprising a hub and a cannula, in which the cannula has a front end projecting from the hub and a back end terminating within the hub.
Conventional injection needles include, as one type, the specific injection needle such as one called "insulin needle" available from Novo Nordisk A/S, which has a specific structure and configuration wherein a cannula having a front end with a sharp bevel and a back end with another sharp bevel inserts in a center hole of a hub in such a manner that the back end projecting inside the hub terminates within the hub (hereinafter, this type of injection needle is merely referred to as injection needle).
In the general manufacturing process of injection needles, a sharp bevel end of a cannula attached to a hub is dipped into a vessel containing a liquid in which silicone oil is diluted with a volatile solution (referred to simply as silicone-containing-liquid in this specification) to apply silicone to the cannula, in order to improve sliding property of the cannula thereby reducing penetration force of the injection needle. In the case of the injection needle mentioned above, however, the normal dipping application causes silicone-containing-liquid to adhere to the hub since the back end of the cannula terminates within the hub and does not project from the hub. Adhesion of silicone-containing-liquid to the hub is undesirable since such adhesion causes problems that silicone-containing-liquid becomes wasteful, and a jig in the next step is contaminated. It further causes problems that the hands of an operator are soiled, or due to slipping of the hands attachment operation becomes difficult, since the hub is such a portion that is held by the hands when attaching an injection needle to a syringe.
Hitherto, application of silicone to the back end of the cannula has been carried out, for example, by a method wherein porous resin having a size smaller than the inner diameter of the hub is impregnated with silicone-containing-liquid, and the back end is pricked into the porous resin.
In the method using resin impregnated with silicone-containing-liquid, however, there are several drawbacks that (1) the application of silicone oil becomes difficult because the diluent in the silicone-containing-liquid evaporates and the composition of silicone-containing-liquid changes such that viscosity of the silicone-containing-liquid becomes too high, (2) contaminant, which is transferred from the cannula to the resin, is liable to adhere to the cannula again, (3) very small pieces of the resin are liable to adhere to the cannula, and the like.
The present invention was made in view of the drawbacks of the conventional method and apparatus for applying silicone to a back end of a injection needle, and an object of the present invention is to provide a method and an apparatus wherein composition of silicone containing liquid does not change substantially, and foreign matter does not adhere to the cannula.